On the day Danbury’s Ryan Fox turned 21 last year, he didn’t head for the fridge or the nearest watering hole. Instead, he went for a walk.

And kept going in a rather Forrest Gump sort of way.

By the time Fox finished, he had walked 21 miles, a coming-of-age stroll to commemorate his birthday. The weather was clear. So was his mind. There was no waist-high snow or three-foot drifts that swallowed every step.

Not yet, anyway.

“I like to do things that challenge me and push me. The hike was kind of a spontaneous thing on my birthday,” said Fox, a graduate student attending the University at Albany. “The Appalachian Trail idea didn’t come until later.”

Fortunately, Fox knows a few things about endurance. A former star distance runner at Danbury High School, Fox also competed in college until a knee injury changed everything.

Well, almost everything. Maybe Fox couldn’t run a marathon last year, but he sure could walk.

Remember those 21 miles on his birthday? Now multiply them by about 100 as you consider the 2,180-mile Appalachian National Scenic Trail. And while you’re at it, ratchet up the degree of difficulty “with an elevation gain and loss equivalent to hiking Mt. Everest from sea level and back 16 times,” according to the Appalachian Trail Conservancy.

“No one personally told me hiking it was a bad idea. I knew zero people who had done it, so I was on my own somewhat,” Fox said during a recent phone interview.

The Appalachian Trail, dubbed the “Footpath of the People” by the U.S. National Park Service, stretches through 14 states. It climbs and dips from Mount Katahdin, the highest peak in Maine at 5,267 feet, to Springer Mountain in Georgia with a summit of 3,782 feet.

“The limits of what people put on themselves is arbitrary. My knee was still pretty messed up when I started,” Fox said. “I knew it would be more of a mental challenge than a physical one, but that’s part of why I wanted to do it.”

For most people — Fox happily self-identifies as “not most people” — this profound exercise in self-examination begins in Georgia in the spring and concludes in Maine five or six months later.

Not being most people, Fox joined the 10 percent of hikers who head the opposite way. Fox also planned to do it faster — in four months — and delay the start of his journey until August, which put him at the mercy of the Great Smoky Mountains near the end of his hike.

“I had committed to work at a summer camp in southern New Hampshire,” Fox explained. “My last day was Aug. 16 and I started the next day from Mount Katahdin.”

But the euphoria of launching a great adventure quickly turned to debilitating pain, nearly ending Fox’s hike in the first 100 miles. Wet feet, soaked shoes and an ambitious schedule hurled him to the hospital.

“The soft tissue on my feet was just getting torn apart,” Fox said. “I had open wounds that were bleeding and oozing.”

Finally, after eight days off the trail — and more than a few folks suggesting he try again another time — Fox grabbed his gear and headed out.

After finishing Maine and New Hampshire, Fox picked up the pace. He averaged more than 20 miles a day pushing through Vermont, Massachusetts, Connecticut, New York and New Jersey.

In Pennsylvania, Fox battled stomach sickness for a week before going through Maryland and Harpers Ferry, West Virginia, the halfway point of the Appalachian Trail.

From there, he spent nearly all of November hiking across Virginia. Despite increasingly frigid temperatures, Fox still averaged almost 20 miles a day.

“I was consistently staying in shelters then, which are more like a lean-to and usually infested with mice. You can hear them crawling around at night,” said Fox, who reached Tennessee by Thanksgiving with winter coming on strong.

Remember that waist-high snow and those three-foot drifts?

Shortly after Fox made his way into Tennessee, a vicious snowstorm in the Smoky Mountains shut down the only road for 70 miles. With the weather deteriorating and his safety at risk, Fox picked up a ride from the Park Service to nearby Gatlinburg, Tennessee. Another driver, a Trail Angel volunteer, drove him to Fontana Dam in North Carolina, where he resumed his hike.

“Unfortunately, I had to jump those last 40 miles of the Smokies,” Fox said. “I’m going to finish them in May. That’s very important to me.”

Fox arrived at Fontana Dam with the end in sight. After grinding it out through North Carolina, he reached Georgia with just 70 miles to Springer Mountain.

A few days later, he walked the last mile of the trail with his father, Irving Fox, who had driven from Danbury to meet him. The calendar read Dec. 19.

“At the end, there’s no cheering crowd waiting there for you,” Fox said. “My friends and family supported me so much, but during the really hard times, it’s up to you. Time passes by so quickly in life. I want to do as many cool things as I can.”

Brian Koonz is a freelance writer and former reporter, editor and columnist for the Hearst Connecticut Media Group.